As a magnetic tape cartridge utilized for an external memory medium for backup of a data of a computer and the like, there is a conventionally known magnetic tape cartridge that satisfies a so-called LTO (Linear Tape Open) standard. Such a magnetic tape cartridge comprises a cartridge case separately formed by a lower half and an upper half, and a single reel winding a magnetic tape is accommodated in the cartridge case. A tape-leading opening for pulling out the magnetic tape is provided at one side of the cartridge case extending over the lower and the upper halves, and a leader pin connected at the end of the magnetic tape is engaged at the tape-leading opening in such a manner that the magnetic tape is pulled out from the opening. Further, an opening for driving the reel is formed in the lower half of the cartridge case so that a hub of the reel is exposed to view from the opening.
A drive device loading the magnetic tape cartridge performs recording and playback of the data by pulling out the leader pin from the cartridge case and winding off the magnetic tape from the reel. Recording and playback of the data is also performed by rotatively driving the hub through the opening for driving the reel of the lower half to rewind the magnetic tape in the reel. The reel rotates only when the magnetic tape cartridge is loaded into the drive device. For the purpose of preventing undesirable rotation of the reel while the magnetic tape cartridge is not loaded into the drive device, a lock plate for locking the reel and a release pad for releasing or disengaging the locked state of the reel are arranged in the cup-shaped hub of the reel.
The lock plate is a disk-like or cup-shaped member and is provided at the lower periphery of the bottom portion with a hub-side engaging portion to be engagable with a corresponding engaging portion projecting from the inner bottom surface of the cup-shaped hub of the reel, and at the upper center of the bottom portion with a half-side engaging portion engaging with an engaging portion projecting from the center of the upper half of the cartridge case. A compression coil spring is positioned between the upper half and the lock plate so that the lock plate is urged by the resilient force of the coil spring and the hub-side engaging portion is brought into engagement with the engaging portion of the cup-shaped hub to thereby lock the reel.
Meanwhile, the release pad is a plate-like member positioned between the inner bottom surface of the cup-shaped hub and the lock plate and substantially in the shape of triangle, quadrangle, star or propeller. At each corner of the release pad that faces proximately to the inner peripheral surface of the cup-shaped hub, a lock releasing pin projects downwardly and extends through the bottom surface of the cup-shaped hub. When the magnetic tape cartridge is loaded into the drive device and the cup-shaped hub is rotatively driven by the reel driving mechanism (not shown) of the drive device, each of the lock releasing pins of the release pad is urged in the direction of the lock plate to press the lock plate toward the upper half against the compression coil spring, thereby releasing the engagement between the hub-side engaging portion of the lock plate and the engaging portion of the cup-shaped hub to unlock the locked state of the reel.
One example of the lock plate and the release pad of a conventional magnetic tape cartridge will be described with reference to FIG. 15. As shown in FIG. 15, the lock plate 10 is a cup-shaped member and is provided at the lower periphery of the bottom portion 10B with a hub-side engaging portion 10A to be engagable with a corresponding engaging portion 11C inwardly projecting from the bottom portion 11B of the cup-shaped hub 11A of the reel 11, and at the inner (upper) center of the bottom portion 10B with a half-side engaging portion 10C engaging with an engaging portion 12 projecting from the center of the upper half of the cartridge case. A compression coil spring 13 is positioned between the upper half and the lock plate 10 so that the lock plate 10 is urged by the resilient force of the coil spring 13 and the hub-side engaging portion 10A is brought into engagement with the engaging portion 11C of the cup-shaped hub 11A to thereby lock the reel 11.
Meanwhile, the release pad 14 is a propeller-shaped plate-like member and comprises a disk-shaped center portion 14A, three arm portions 14B extending outwardly from the center portion 14A, and three lock releasing pins 14C extending downwardly from the respective ends of the arm portions 14B. Each lock releasing pin 14C has a rectangular outer profile at its lower end surface 14D. The three lock releasing pins 14C are inserted into corresponding three rectangular through-holes 11D formed in the bottom portion 11B of the cup-shaped hub 11A and the lower end surfaces 14D project from the lowermost surface of the bottom portion 11B of the cup-shaped hub 11A. When the magnetic tape cartridge is loaded into the drive device and the cup-shaped hub 11A is rotatively driven by the reel driving mechanism (not shown) of the drive device, each lower end surface 14D of the lock releasing pins 14C is urged toward the upper half to press the lock plate 10 toward the upper half against the compression coil spring 13, thereby releasing the engagement between the hub-side engaging portion 10A of the lock plate 10 and the engaging portion 11C of the reel 11 to unlock the locked state of the reel 11.
Herein, as a general structure of the reel, a flange is welded at the opening side of the cup-shaped hub. Since the flange is normally spigot-fitted into the inner peripheral wall of the cup-shaped hub, the inner periphery of the flange slightly extends inwardly compared with the inner peripheral wall of the cup-shaped hub. For this reason, when the release pad is assembled with the cup-shaped hub of the reel during the assembly of the magnetic tape cartridge, the release pad is tilted and inserted into the hub so as not to contact with the inner periphery of the flange, and then dropped in a certain position with each of the lock releasing pins positioned with respect to the through-holes formed in the bottom portion of the cup-shaped hub.
When doing so, normally, the release pad is held with each lock releasing pin facing downward and one side (edge) of the pad body connecting two corners thereof being tilted forwardly. In other words, the release pad is inserted into the cup-shaped hub from one side (edge) of the pad body with the front side (edge) thereof being lowered, and thereafter the rear side is lowered to reduce gradually the inclination angle of the release pad. At the same time, positioning is carried out between two of the front side lock releasing pins and the plurality of through-holes formed in the bottom portion of the cup-shaped hub. When the release pad is dropped onto the bottom surface of the cup-shaped hub while retaining the relative position of the release pad, each of the lock releasing pins pierces through the corresponding through-holes of the cup-shaped hub so as to ensure the assembly of the release pad and the cup-shaped hub.
Meanwhile, during the assembly of the magnetic tape cartridge as illustrated in FIG. 15, if a robot assembles the release pad 14 with respect to the cup-shaped hub 11A of the reel 11, the robot holds the release pad 14 and inserts the lock releasing pins 14C into square holes 11D as the through-holes of the cup-shaped hub 11A. In this event, in order to carry out positioning of the lock releasing pins 14C with respect to the square holes 11D, at least either positions of the lock releasing pins 14C or positions of the square holes 11D are calculated through image processing.
In the image processing, for example, when the square holes 11D of the reel 11 are positioned to a certain position, the square holes 11D as the through-holes are pictured by a stationary camera for image processing and each central point of the square holes 11D is calculated by the image processing device. And based on these calculated central points, the deviation of the angle from the regular position of the reel 11 is calculated. The reel 11 is rotated by a device arranged below the belt conveyor in such a manner that the deviation of the angle can be corrected and positioning can be carried out. Also, when the lock releasing pins 14C of the release pad 14 are positioned to a certain position, the lower end surfaces 14D thereof are pictured by the camera, and based on the picture data, the robot rotates the release pad 14 to carry out positioning.
However, since the through-holes are arranged proximately to the inner peripheral wall of the cup-shaped hub pursuant to a circumferential arrangement having a certain diameter defined by LTO standard, it is difficult to ensure positioning of the lock releasing pins of the release pad, which are inserted into the cup-shaped hub in a tilted manner, with respect to the through-holes of the reel. If the assembly is carried out by the use of an assembling robot, the release pad would be assembled defectively.
Further, pluralities of reinforcement ribs are usually projecting at the inner peripheral wall of the cup-shaped hub, and especially, the ribs arranged proximately to the through-holes are adjacent to the pad body of the release pad when the release pad is assembled with the cup-shaped hub. Therefore, when the release pad is inserted into the cup-shaped hub from one side (edge) of the pad body with the front side (edge) thereof being lowered, one front side (edge) of the pad body abuts to the ribs and positioning of the two lock releasing pins with respect to the corresponding through-holes would be insufficient, leading to defective assembly of the release pad. This is more serious when assembly of the release pad is carried out by the use of an assembling robot.
Meanwhile, as shown in FIG. 15, since in the conventional reel, the outer profile of each square hole 11D and the outer profile of the lower end surface 14D of each lock releasing pin 14C are in the shape of a rectangular, if the square holes 11D of the cup-shaped hub 11A and/or the lower end surfaces 14D of the release pad 14 are rotated and out of position from the certain regular position, the stationary camera for image processing pictures these outer profiles differently. For this reason, calculating the central points of the square holes 11D and the lower end surfaces 14D that are out of position from the certain regular position becomes complicated and it is difficult to prepare an image processing program.
In view of the above, the first object of the present invention is to provide a magnetic tape cartridge wherein assembly of the release pad is reliably carried out by an assembling robot. Further, the second object of the present invention is to provide a magnetic tape cartridge wherein the outer profile of each through-hole or the outer profile of each lock releasing pin is always the same irrespective of the position of the cup-shaped hub and the release pad so that the image processing program can be readily made.